1. Field of the Invention
The present invention relates to the developer-regulating member (member for regulating a thickness of a developing agent) of a development device for visualizing a latent electrostatic image by developing a latent electrostatic image formed on an image-holding member. The present invention relates also to a development device and a process cartridge employing the developer-regulating member, and a process for producing the developer-regulating member.
2. Related Background Art
The developer-regulating member regulates the layer thickness of a developing agent (developer) on a developer-feeding member for carrying the developer onto an electrophotographic sensitive member. More specifically, the developer-regulating member is brought into pressure contact with a developer-feeding member to allow the developer to pass through the gap between the developer-regulating member and the developer-feeding member to form a thin layer on the developer-feeding member, and to give a frictional charge (triboelectric charge) to the developer for developer a latent image.
Elastic blades, as the developer-regulating member, have been proposed in which a rubber blade as the developer-regulating member and a metal holder are integrated into one body.
The elastic blade of such a constitution is produced by injection molding because of the low cost and short time for production. In the injection molding, a holder as a supporting plate is placed in a metal mold, a rubber material is injected into the metal mold, and the injected rubber material is cured by heating. The molding temperature is usually controlled so that the metal mold is kept at 200.degree. C. and a liquid rubber kept at about 30.degree. C. is injected to thermally cure the rubber. In the molding of the rubber elastomer with the metallic holder in integration, a hot adhesion primer is suitably used for improving the adhesion between the less adhesive rubber, such as a silicone rubber, and the metal.
The conventional developer-regulating member may cause irregularity in the image density owing to nonuniform pressure contact of the rubber elastomer with a developer-feeding member. This nonuniform contact results from the two causes discussed below.
The first cause is now described. In the integral injection molding, the rubber elastomer warps convexly along the lengthwise direction as shown in FIG. 2 by the upper arrow mark. The contact portion to be brought into pressure contact with a developer-feeding member is warped convexly because the linear expansion coefficient of the rubber elastomer is significantly different from that of the metallic holder. A steel plate has a linear expansion coefficient of 10.times.10.sup.-6, whereas a thermosetting liquid silicone rubber, a typical rubber material for the developer-regulating member, has a linear expansion coefficient of 77.times.10.sup.-6. Therefore, the dimension of thermal contraction differs between the metallic holder and the rubber elastomer blade to cause deformation of the rubber elastomer blade integrated with the metallic holder. Furthermore, in curing of the rubber elastomer, internal stress becomes nonuniform to also cause deformation of the rubber elastomer.
Further, the cross-sectional shape of the rubber elastomer blade at a plane perpendicular to the lengthwise direction of the development blade is not symmetrical, the shape thereof at the toner container side being different from the shape at the side of contact with the developer-feeding member (FIG. 3). Such a shape factor causes the above convex warpage.
In regulating the electric charging and toner application by using such a convexly warped developer-regulating member, the pressure of contact of the rubber blade with the developer-feeding member is higher at both end portions in the lengthwise direction of the developer-feeding member. Thus, in printing with a copying machine or a printer, the toner layer is thinner at the end portions of the sleeve owing to the higher pressure, resulting in a lower density of the formed image at both end portions.
The second cause of the irregularity in image density is now described. One type of the developer-regulating member for suitable control of the contact pressure has the blade thickness varying in the lengthwise direction and in the vertical direction. FIG. 13 shows an example thereof. This developer-regulating member has a slanting face portion of the rubber elastomer at the side reverse to the pressure-contacting side with the thickness of the rubber elastomer increasing toward the metallic holder. In injection molding of the developer-regulating member of such a structure, the molded member warps owing to the linear expansion coefficient difference between the metallic holder and the rubber elastomer. This warpage is caused in two directions, convexly at the side of pressure contact with the developer-feeding member as mentioned above, and concavely as the entire rubber elastomer (shown by the arrow mark in FIG. 13). This warpage at the tip portion of the rubber elastomer can be corrected by cutting to flatten the face. However, the concave warp at the taper portion 7 in FIG. 13 cannot be corrected by machining. With such a developer-regulating member being warped at the taper portion, the contact pressure varies in the lengthwise direction on pressure contact with the developer-feeding member, with higher contact pressure at both end portions of the pressure contact, causing irregularity of the image density at the blade end portions.
From the above two causes, a conventional developer-regulating member causes irregularity in the image density, owing to nonuniform pressure contact of the rubber elastomer blade with the developer-feeding member.